The term "vitamin A" refers to a large number of related compounds: preformed retinol (an alcohol) and retinal (an aldehyde). Vitamin A deficiency is common in teenagers, in lower socioeconomic groups, and in developing countries (Combs 1998). Furthermore, some studies indicate that diabetic patients are at an increased risk for vitamin A deficiency (Queiroz et al. 2000). This deficiency may manifest as night blindness, immune deterioration, birth defects, or decreased red blood cell production (Higdon 2003). Purported therapeutic uses for vitamin A include diseases ofthe skin, acute promyelocytic leukemia, and viral infections.
Retinoids have been used as pharmacologic agents to treat disorders of the skin. Psoriasis, acne, and rosacea have been treated with natural or synthetic retinoids. Moreover, retinoids are effective in treating symptoms associated with congenital keratinization disorder syndromes. Therapeutic effects stem from its antineoplastic activity (Brzezinska-Wcislo et al. 2004). Patients suffering from these illnesses may be supplementing with vitamin A and their dosages should be explored.
Vitamin A may increase anticoagulant effects of warfarin (Harris 1995). This interaction could increase the risk of bleeding complication in these patients. Bleeding complications may therefore be avoided by informing the patient about this effect preoperatively.
Excess vitamin A intake during pregnancy, as well as deficiency, may lead to birth defects. For this reason, pregnant woman who are not vitamin A deficient should not consume more than 2,600 IU/day of supplemental retinol (Binkley and Krueger 2000).
Patients using isotretinoin and pregnant women taking valproic acid are likewise at increased risk for vitamin A toxicity (Higdon 2003, Nau et al. 1995). Finally, alcohol consumption decreases the liver toxicity threshold for vitamin A, thereby narrowing its therapeutic window in alcoholics (Leo and Lieber 1999).
Was this article helpful?